How to reset the code?

we bought a house with an alarm systems, the ex owner forgot the code, and there is no sign on the pannel, we do not know which company installed it;only on the back of the pannel, it said "KP1100 B/L 81" . sometimes when power went off, it kept ring; very annoying. we don't know how to stop it. could someone know how to reset the code? many thanks.